Removal of carbon monoxide



United States Patent 3,383,164 REMOVAL OF CARBON MONOXIDE Allan C.Harkness, Vancouver, British Columbia, Canada, assignor toAllis-Chalmers Manufacturing Company, Milwaukee, Wis.

N0 Drawing. Continuation-impart of application Ser. No. 176,914, Mar. 2,1962. This application May 27, 1965, Ser. No. 459,429

12 Claims. (Cl. 23-2) This is a continuation-in-part of my now abandonedUnited States application Ser. No. 176,914, filed Mar. 2, 1962.

The present invention relates generally to the removal of carbonmonoxide from gases and more particularly to improved compositions andmethods employing a novel catalytically activated mechanism for removingcarbon monoxide from gas streams in a rapid and easy manner.

While it has heretofore been known that carbon monoxide could beoxidized by an acidified aqueous solution of potassium permanganateaccording to the reaction:

the reaction is thermodynamically spontaneous, but kinetically sluggishand because of its slow rate it is not commercially feasible.

Also heretofore known is that solid silver permanganate oxidizes carbonmonoxide, but solid silver permanganate is expensive to use because onemole of silver is necessarily present for every mole of thepermanganate.

Carbon monoxide (CO) is a toxic gas even in minute quantities. I havediscovered a process for purifying a CO contaminated gas stream bypassing it through an acidified permanganate (MnO solution to oxidizethe CO to carbon dioxide (CO I have found that the oxidation rate isvastly increased by inclusion of minute catalytic quantities of silverion (Ag+) and/ or mercuric ion (Hg*') in the MnO; solution.

Accordingly, the general object of my invention is to provide a methodfor the oxidation of carbon monoxide to carbon dioxide in a gas-liquidphase reactiion using a non-noble source of permanganate and a catalyticamount of either silver or mercuric ion.

Still another object of my present invention is to provide a method forremoving carbon monoxide from gaseous streams which lends itself toreasonably small installations while at the same time providing a volumewhich is commercially feasible.

These and still further objects as shall herein-after appear arefulfilled by the present invention in a totally unexpected manner as maybe readily discerned from the following detailed description of anexemplary embodiment of the present invention.

In order to conveniently follow the kinetics of my catalyzed reaction, Ilowered the silver ion concentration to about 1 1() M and worked withtemperatures ranging from 0-25" C. The rate of carbon monoxide oxidationin my reaction is described by the following rate expression:

wherein: k is the rate constant of the uncatalyzed reaction (e.g., 0.52M- sec. at 25 C.); k is the rate constant of the catalyzed reaction (Msecf and [X] is the concentration of the catalyst ion (M). As usedherein, M signifies moles/ liter.

ice

While both silver and mercuric ions have been found catalytic for thereaction, silver ions are considerably more effective than the mercuricions. Thus, at 0 C. in

1 M perchloric acid, k for silver ions is 1.10 10 M sec. while k formercuric ions at 0 C. in 1 M perchloric acid is 1.06 10 M- see- Informulating my solution, any soluble permanganate may be used to providethe desired level of permanganate ion concentration although thepermanganates of the more costly metals such, for example, as cadmium,zinc and the like, are avoided for economic reasons. The permanganatesof the alkali and alkaline earth metals perform very well and carry acost which is practical. For this reason, their use is recommended.

Similarly, my tests show that any simple soluble silver or mercuric saltmay be employed to provide the desired catalyst ion concentration. Thus,for example, silver nitrate; mercuric nitrate; silver perchloroate;mercuric perchlorate; silver sulfate and mercuric sulfate all performsatisfactorily. It has been noted that mercurous salts may also beemployed but, as is apparent, the effective catalytic ion will still bemercuric for the permanganate would promptly oxidize the mercurous ionto the mercuric ion. As before, the effective catalytic activation wouldbe obtained.

As soluble is used herein with respect to my catalytic reagents, itmeans possessing sufiicient solubility to provide -a small but effectiveion concentration. An effective ion concentration is that which issufficient, in Equation b above, to provide (k [X]) with a value greaterthan k at the reaction temperature. Thus, at 25 C. it will be necessaryfor (k [X]) to be greater than 0.52 M secthat is, in the case of silver,X must be greater than 3.71 X10 M. It also becomes apparent that certainsilver salts which are normallyconsidered insoluble are stillsufficiently soluble for use in the practice of this invention. Thus,silver chloride, with its solubility of about 1x10 M, while generallyconsidered insoluble, provides sufficient ion concentration to beoperable in the invention.

The solvent I prefer to employ is aqueous perchloric acid although anysolvent capable of providing a pH of seven or less, and preferably fouror less, which is com patible with permanganate, i.e., is not oxidizedby it, and which does not complex with the metal ions to a substantialextent will be satisfactory. Thus, at room temperature, sulfuric, nitricand hydrochloric acids may also be employed as the solvents. Of these,sulfuric acid is referred.

My results further indicate an increased activity resulting fromincreased temperature although the instantaneous occurrence of thereaction at room temperatures renders it generally unnecessary tooperate at temperatures in excess of room temperatures.

Thus, k (see Equation b above) for silver ions at 0 C. is 1.10X10 M"sec.- while this becomes 1.40 10' M- secf at 25 C. Similarly, k for themercuric ions is 106x10 M sec. at 0 C. and 240x10 M secr at 25 C.

In the preferred practice of the present invention an excess ofpermanganate is used so as to maintain the permanganate ionconcentration in the solution relatively constant whereby the reaction(see b above) becomes a pseudo-first order reaction and the reactionrate is directly proportional to the concentration of carbon monoxide.Thus, knowing the volume of the gas to be treated and the amount ofcarbon monoxide to be removed, the size of the reaction vessel and theamount of catalyst to be used can be readily calculated using Equation babove.

The activation energy of my reaction, derived by calculating the rateconstant at various temperatures and employing the Arrhenius equation,to wit:

(c) log k :A-E/RT where:

k is the rate constant;

A is an equation constant;

E is activation energy;

R is the gas constant, and

T is the temperature in degrees absolute;

E is 1.8 kcals./mole for Ag'*, and 7.0 keel/mole for Hgd-d;

E for the uncatalyzed reaction is 13.6 kcal./mole.

Of course in the practice of my invention, silver ion and mercuric ioncan be used either singly or in combination to provide the catalyticactivity.

Now utilizing my discovery, a continuous process that does not requireinterruption to recharge the system with either oxidant or catalyst, orto remove spent oxidant has been provided. In practicing my invention asa continuous process, a gas stream of carbon monoxide contaminated gasis passed through a scrubber containing the catalytic solution. The COwhen scrubbed with the acidified permanganate solution containing acatalytic quantity of either silver ion, mercuric ion or a mixture ofsilver ion and mercuric ion oxidizes the CO to C The purified gas streamis passed out of the system, while the catalytic solution can bedirected through a filterin means to trap and remove the precipitate ofmanganese dioxide before returning to the scrubber. Fresh permanganate,to replenish that lost by reduction to manganese dioxide, is added tothe catalytic solution.

From the foregoing it becomes apparent that a unique and etfectivesystem for the removal of carbon monoxide has been described whichfulfills all of the aforestated objectives to a remarkably unexpectedextent. it further is apparent that a system utilizing a gas-liquidphase reaction has been described which may be employed either in gasanalysis or in the purification of recycling exit gases employed incatalytic hydrogenation. Other beneficial applications are obvious fromthese teachings which require only that the gas stream containing carbonmonoxide be passed through a solution containing permanganate ionshaving a pH of seven or less and containing a molar excess ofpermanganate ions activated by a small but effective amount of catalystselected from the group consisting of the ions of silver, mercuric andmixtures of these.

It is, of course, understood that such modifications, alterations andapplications as may occur to one skilled in the art from a considerationof this disclosure are intended within the spirit of the presentinvention, especially as it is defined by the scope of the claimsappended hereto.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. The method of removing carbon monoxide from a gaseous streamutilizing a gas-liquid phase reaction comprising forming an aqueoussolution containing permanganate ions; adjusting the pH of said solutionto a value not exceeding 7; adding to the solution a catalytic reagentto provide said solution with a small but effective amount of ionsselected from the group consisting of silver ion and mercuric ion; andcontacting said gaseous stream with said solution whereupon the carbonmonoxide in said stream is substantially completely and rapidly oxidizedto carbon dioxide, and removing said now substantially carbon monoxidefree gaseous stream from contact with said solution.

2. The method of removing carbon monoxide from a gaseous streamutilizing a gas-liquid phase reaction comprising forming an aqueoussolution containing permanganate ions; adjusting the pH of said solutionto a value not exceeding 7; adding to the solution a catalytic reagentto provide said solution with a small but effective amount of silverions; and contacting said gaseous stream with said solution whereuponthe carbon monoxide in said stream is substantially completely andrapidly oxidized to carbon dioxide, and removing said now substantiallycarbon monoxide free gaseous stream from contact with said solution.

3. The method of removing carbon monoxide from a gaseous streamutilizing a gas-liquid phase reaction comprising forming an aqueoussolution containing permanganate ions; adjusting the pH of said solutionto a value not exceeding 7; adding to the solution a catalytic reagentto provide said solution with a small but effective amount of mercuricions; and contacting said gaseous stream with said solution whereuponthe carbon monoxide in said stream is substantially completely andrapidly oxidized to carbon dioxide, and removing said now substantiallycarbon monoxide free gaseous stream from contact with said solution.

4. In a continuous process for purifying a carbon monoxide contaminatedgas strcarn, the steps comprising: passing said carbon monoxidecontaminated gas stream into a scrubber means for intimately contactingsaid gaseous stream with an acidified permanganate solution containing aquantity of ions selected from the group consisting of silver ion andmercuric ion in a concentration less than the concentration ofpermanganate ion; passing the now substantially carbon monoxide freegaseous stream from said scrubbing means; cycling the permanganatesolution from the scrubber through a filtration means for removinginsoluble manganese dioxide from the permanganate solution; and addinsufiicient permanganate to replenish that lost through reduction.

5. In a continuous process for purifying a carbon monoxide contaminatedgas stream, the steps comprising: passing said carbon monoxidecontaminated gas stream into a scrubber means for intimately contactingsaid gaseous stream with an acidified permanganate solution containing aquantity of silver ions in a concentration less than the concentrationof permanganate ion; passing the now substantially carbon monoxide freegaseous stream from said scrubbing means; cycling the permanganatesolution from the scrubber through a filtration means for removinginsoluble manganese dioxide from the permanganate solution; and addingsufiicient permanganate to replenish that lost through reduction.

6. In a continuous process for purifying a carbon monoxide contaminatedgas stream, the steps comprising: passing said carbon monoxidecontaminated gas stream into a scrubber means for intimately contactingsaid gaseous stream with an acidified permanganate solution containing aquantity of mercuric ions in a concentration less than the concentrationof permanganate ion; passing the now substantially carbon monoxide freegaseous stream from said scrubbing means; cycling the permanganatesolution from the scrubber through a filtration means for removinginsoluble manganese dioxide from the permanganate solution; and addingsufiicient permanganate to replenish that lost through reduction.

7. In a continuous process for purifying a carbon monoxide contaminatedgas stream, lthe steps comprising: passing said carbon monoxidecontaminated gas stream into a scrubber means for intimately contactingsaid gaseous stream with an acidified permanganate solution containing asmall but eifective quantity of ions selected from the group consistingof silver ion and mercuric ion; passing the now substantially carbonmonoxide free gaseous stream from said scrubbing means; cycling thepermanganate solution from the scrubber through a filtration means forremoving insoluble manganese dioxide from the permanganate solution; andadding sutficient permanganate to said permanganate solution toreplenish that lost through reduction.

8. The method of purging a gaseous stream of carbon monoxide contaminantutilizing a gas-liquid phase reaction comprising: forming the liquidphase containing an aqueous solution of an alkali metal permanganate;adding sufficient perchloric acid to said solution to adjust the pH to avalue not exceeding 7; adding to said pH adjusted solution a catalyticreagent sufficient to provide said solution with a concentration of ionsselected from the group consisting of silver, mercuric, and a mixture ofsilver and mercuric, said concentration less than the concentration ofpermanganate ions in said solution; intimately contacting the gaseousphase carbon monoxid contaminated gaseous stream with said liquid phasewhereby said carbon monoxide is substantially instantaneously oxidizedto carbon dioxide, and removing carbon monoxide free gaseous phase fromsaid liquid phase.

9. The method according to claim 8 in which said catalytic reagent isselected from the group consisting of silver perchlorate, mercuricperchlorate, silver nitrate, mercuric nitrate, silver sulfate, mercuricsulfate, and mixtures of at least two compounds of said group.

11). The method according to claim 8 in which said alkali metalpermanganate is potassium permanganate.

11. The method according to claim 10 in which said catalytic reagent issilver perchlorate.

12. The method according to claim 10 in which said catalytic reagent issilver nitrate.

Rei'erences Cited UNITED STATES PATENTS 2,657,182 10/1953 K'atz 232 X2,876,507 3/1959 Kuehner et al. 2358 OTHER REFERENCES Mellor, AComprehensive Treatise on Inorganic and Theoretical Chemistry, Longmans,Green & 00., New York, N.Y., volume 12, 1932, pages 297 and 332.

OSCAR R. VERTIZ, Primary Examiner.

20 E. C. THOMAS, Assistant Examiner.

1. THE METHOD OF REMOVING CARBON MONOXIDE FROM A GASEOUS STREAMUTILIZING A GAS-LIQUID PHASE REACTION COMPRISING FORMING AN AQUEOUSSOLUTION, CONTAINING PERMANGANATE IONS; ADJUSTING THE PH OF SAIDSOLUTION TO A VALUE NOT EXCEEDING 7; ADDING TO THE SOLUTION A CATALYTICREAGENT TO PROVIDE SAID SOLUTION WITH A SMALL BUT EFFECTIVE AMOUNT OFIONS SELECTED FROM THE GROUP CONSISTING OF SILVER ION AND MERCURIC ION;AND CONTACTING SAID GASEOUS STREAM WITH SAID SOLUTION WHEREUPON THECARBON MONOXIDE IN SAID STREAM IS SUBSTANTIALLY COMPLETELY AND RAPIDLYOXIDIZED TO CARBON DIOXIDE, AND REMOVING SAID NOW SUBSTANTIALLY CARBONMONOXIDE FREE GASEOUS STREAM FROM CONTACT WITH SAID SOLUTION.